1. Field of the Invention
The present invention relates to a support suitable for a lithographic printing plate having a photosensitive and/or thermosensitive image recording layer and a presensitized plate using the support for a lithographic printing plate. More particularly, the present invention relates to a support for a lithographic printing plate suitable for the formation of a thermal negative type recording layer and a presensitized plate using the support for a lithographic printing plate.
2. Description of the Related Art
In recent years, with the development of an imaging technology, attention has been drawn to a direct plate making technology where a narrowed laser beam is scanned on a printing plate to directly form a character manuscript, an image manuscript or the like on the printing plate without using a film manuscript.
In a so-called thermal negative type lithographic printing plate where a photothermal conversion takes place in a recording layer and a negative image is formed by lowering an alkali-solubility of the recording layer by heat generated, which is the representative aspect of the direct plate making technology, since heat is generated by photothermal conversion agents such as infrared absorbent in the recording layer by irradiating a laser beam and an image formation reaction is triggered by heat, the following problems occur if an image formation reaction by heat is not sufficient.
On an aluminum support on which graining is performed and an anodized layer is formed, heat generated in the vicinity of an interface between the support and the recording layer transfers to inside the support before an image formation reaction sufficiently progresses, since the thermal conductivity of the support is significantly higher than that of the recording layer. Then, since the hardening reactivity of the recording layer particularly at the interface between the support and the recording layer is not sufficient, the contact characteristics of an image area with the support is not sufficient, thus press life occasionally deteriorates.
In addition, if the sensitivity of a solution shown by the conductivity of a developer becomes high, even the image area obtained after hardening reaction, which is hardly melted by nature, is melted. Thus, an inadequate inking may occur and the deterioration of press life may be caused by the problem of the insufficient hardening reaction of the recording layer at the interface. This phenomenon is attributable to the image formation mechanism of the thermal negative type and it is considered that the phenomenon is caused by the hardening reaction mechanism of the recording layer at the time of heating, particularly the insufficiency of the hardening reaction in the vicinity of the interface between the support and a recording layer.
As a means to solve these problems, it is general to perform heat treatment after exposure in order to accelerate hardening reaction at the exposure area of the recording layer. However, since special equipment is required and the process is complicated, it is the status quo that the industry hopes to have a negative type lithographic printing plate capable of forming a better image dispensing with performing a post-heat treatment like this.
Furthermore, in the thermal negative type recording layer where an image is formed by a laser exposure, the following problems exist.
Since the surface of the support is exposed and becomes a hydrophilic area when the unhardened recording layer of a non-exposed area (a non-image area) is removed by a developer, scum tends to develop easily at the non-image area due to the attachment of an undesired ink-receptive ink at the time of printing if hydrophilicity of the support surface is not adequate. Although as a countermeasure to this problem, silicate treatment or the like is performed on the surface of the support after anodizing treatment is performed thereon for the purpose of enhancing the hydrophilicity, a further improvement is required.
In addition, there is also a problem that if a developer exhausts and the sensitivity of the solution shown by the conductivity lowers, the solubility of the recording layer deteriorates and a residual layer is generated, and scum tends to develop easily at the non-image area.
As the means to solve these problems, for example, various undercoating treatments and the like are reviewed. However, each trial cannot reach a sufficiently satisfactory level.
On the other hand, as a recent market trend, users have a strong demand that they would like to use equipment at the lowest possible output power or the like, since the time of exposure is to be shortened in order to enhance productivity and to extend the service life of a laser more. Users strongly seek for a high-sensitivity thermal negative type presensitized plate capable of efficiently using the energy of a laser beam for an image formation reaction, even if the energy of the laser beam is lowered.